The Colorado River Basin provides freshwater to more than 40 million people within the semi-arid southwestern United States, including major cities such as Las Vegas and Los Angeles. However, between 2000 and 2021 the basin experienced a megadrought (a severe drought lasting multiple decades), which researchers have suggested likely would not have occurred if it were not for anthropogenic climate change. In particular, during 2020 and 2021, the river basin recorded the driest 20-month period since 1895 and the lowest river flow since 1906.
Dr. Benjamin Bass and colleagues at the University of California aimed to identify how precipitation and runoff within the basin have changed since the 1880s, in line with a 1.5°C increase in temperature over the same period. New research, published in Water Resources Research, identified a 10.3% decrease in runoff within the basin as a direct result of anthropogenic warming and vegetation changes in the landscape, meaning available water resources to support the local population have declined 2.1 km3.
Furthermore, the scientists found that snowpack regions were significantly impacted by aridification, exacerbating the decline in runoff to twice that of neighboring areas. Though snowpack regions constitute only 30% of the Colorado River drainage basin, the aridification has led to an 86% decrease in runoff (losing 1.2 km3 of water per °C of warming).
This is likely to worsen due to albedo feedback, whereby the declining snow reduces the lighter ”white” snow surface to reflect heat from solar insolation, instead exposing more of the land to absorb heat and ultimately increasing temperature further which causes more snow to melt and so the feedback loop continues.
Using Global Climate Models and historical data, the researchers performed simulations to assess the trends in runoff with anthropogenic changes, as well as predicting the scenarios if human influence is removed. They found that the drainage basin runoff has decreased 1.2 km3 since 1954, but suggest that runoff would have actually increased by 0.9 km3 had the influence of global warming and elevated CO2 not occurred.
2023-07-29 16:00:04
Original from phys.org rnrn